The present invention relates to a novel process for the biologically mediated treatment of solid and liquid organic wastes, paiticularly animal farm wastes, including the removal of nutrients from such wastes, such as, for example, phosphorous and nitrogen.
Everyday, organic waste streams are created that need to be treated in some form or manner before they are disposed of. For example, organic waste streams in conventional municipal waste and wastewater plants, food manufacturing facilities, industrial factories, and animal farms are typically treated either physically, chemically, and/or biologically before combining the effluent(s) with a water body, land applying the effluent(s), or disposing of the effluent(s) in an alternative manner, such as by removal from the site for further treatment elsewhere.
Organic waste treatment technologies have progressed significantly in recent years due, in part, to increased public awareness, lobbying, legislation and regulatory oversight. In some instances, treatment technologies have been developed upon the realization that entirely new and useful products could be created from the wastes thereby generating new business opportunities for technology innovators. Often times, new or improved technologies are created for purely economic reasons.
Presently, most treatment technologies for organic wastes typically include some form of biological treatment wherein biological organisms stabilize organic matter and remove soluble and/or nonsettleable colloidal solids to reduce the content of microbial substrates (nutrients such as phosphorus, sulfur and particularly nitrogen and other organic biodegradable materials as measured by the total biochemical oxygen demand (BOD) test). The microbial substrates, particularly if left untreated, are known to pollute surface and subsurface water supplies and negatively impact air and soil quality. Suspended growth processes, attached-growth processes and combined suspended and attached growth processes are used for biological treatment of organic wastes to reduce substrate quantities in the treated effluents. Often times, waste streams and the microbial substrates therein are also subjected to additional treatment processes prior to the disposal of process effluents such as, for example, screening, digestion, composting, disinfection, chemical precipitation, and/or phosphorous removal.
With increasing human population density, municipal wastewater treatment facilities, animal farming facilities, and organic industrial treatment and food processing facilities have come under increasing pressure to upgrade, modify, or supplement their treatment processes to improve the quality of system effluent discharges as well as the air in and around such facilities to further protect the environment, and human and animal health. A particularly persistent problem addressed by the present invention is the treatment of animal excrement containing high concentrations of microbial substrates which, in typical animal treatment systems, not only pollute surface and subsurface water supplies, but also negatively impact air and soil quality. The effluent discharges from these animal treatment systems oftentimes contain undesired amounts of available nitrogen and phosphorous which has been linked to detrimental effects in water bodies such as, for example, accelerated eutrophication and aquatic growths. Further, present treatment alternatives for organic waste streams, such as animal excrement, frequently generate and exacerbate the offensive odors and emissions of atmospheric pollutants.
The input to an organic waste biological treatment process usually contains concentrations of phosphorus and other nutrients such as, for example, nitrogen. This will hold for flowable organic waste streams or for non flowable wastes, such as scrapped fresh manure, which are converted into an aqueous stream by mixing with a recycle stream from a treatment process. For municipal wastewaters, the typical influent phosphorus (P) to nitrogen (N) load ratio (the “P/N Ratio”) is about 0.18. Metcalf & Eddy, Wastewater Engineering—Treatment and Reuse, 4th Ed., Tchobanoglous, George et al., McGraw-Hill, Inc. (2003). P/N Ratios for animal farm wastes are typically about 0.18 (dairy) to 0.30 (swine and layers). ASAE Standard D384.1, 2003. Industrial waste and food industry waste P/N Ratios are less consistent than those for municipal or animal wastes and largely depend on the products and the processes. Some of the nutrients in such organic inputs will be incorporated into the microbial cell mass as a result of the biological treatment process and may be removed from treatment systems as a component of the solids (sometimes referred to as sludge). The portion of the nutrients remaining in the waste stream (whether converted or unconverted by the biological treatment process) will be discharged with the liquid effluent.
In some processes, the amount of a single nutrient can be a limiting factor to the biological treatment process and nearly all of that nutrient is converted and incorporated into the microbial cell mass leaving little, if any, portion of that nutrient in the process liquid effluent. In conventional biological wastewater treatment processes where the BOD and COD concentrations are not limiting, and when the P/N Ratio is appropriately low relative to the requirements of normally growing microbial populations, the vast majority of the phosphorus will be assimilated into biomass and the phosphorus in the liquid effluent will in turn be relatively low. This will generally be true if the P/N Ratio is less than about 0.16 (as long as no significant nitrification and denitrification is occurring in the system in which case nitrogen gas is typically released increasing the P/N Ratio that can be treated), since this is the P/N Ratio commonly found in slowly growing microbial cells. In effect, the phosphorous and nitrogen in the wastewater treatment system is assimilated into microbial cells.
In the low oxygen organic waste biologically mediated conversion system for an organic waste described in U.S. Pat. No. 6,689,274 (Northrop et al.), in order to accomplish a similar result for biological conversion of phosphorous and nitrogen, the P/N Ratio needs to be somewhat lower than 0.16 because significant amounts of nitrogen are discharged to atmosphere as dimolecular nitrogen gas and hence is not available for incorporation into microbial cells. Thus, P/N Ratios of about 0.07 or less would normally be required in the organic influent waste stream to achieve equivalent low effluent phosphorus discharges as seen in conventional biological treatment systems. The phosphorous content in the treated effluent depends upon the incorporation of phosphorous into microbial cells and other settleable and/or suspended solids and then separating those cells and solids from that effluent by collecting them as a portion of the harvested humus material generated by the process. Any phosphorus not converted into insoluble and/or particulate form, as well as any insoluble and/or particulate nutrients not collected in the harvested humus material will be discharged in the system effluent. On average, phosphorous removal by biological treatment processes with sludge wasting may range from 10 to 30 percent of the influent amount. Metcalf & Eddy, Wastewater Engineering, Treatment, Disposal, Reuse, 3rd Ed., Tchobanoglous, George et al., McGraw-Hill, Inc. (1991) at p. 726. According to the process described in U.S. Pat. No. 6,689,274, low effluent discharges of phosphorus would contain less than about 50 percent of the influent phosphorus load (greater than about 50 percent removal). Preferable discharges would contain less than about 20 percent of the influent phosphorus load (greater than about 80 percent removal).
When the influent waste stream to a biological wastewater treatment process contains P/N Ratios which are higher, sometimes substantially higher, than 0.16, the resulting concentration of soluble phosphorous in the effluent stream may be higher than desired and it is sometimes necessary and/or desirable to lower such effluent phosphorus discharges. One method known in the art to try to lower such effluent phosphorous discharges is the addition of an anaerobic zone to an aerobic wastewater biological treatment process. The expected increase in the phosphorus content of the resultant biomass and sludge is supposed to reduce effluent phosphorus discharges. This phosphorous conversion process is generally known as the “Bio-P” process and the conversion mechanism is understood to be as follows:
A community of Phosphorus Accumulating Organisms (“PAOs”), when exposed to alternating aerobic and anaerobic environments, will take up excess amounts of phosphate ions and store them as polyphosphate. When these PAOs encounter anaerobic conditions they will use the energy stored in the polyphosphate, thereby decreasing their polyphosphate stores, and will accumulate acetate or other volatile fatty acids, storing these compounds in polymer form, usually as polyhydroxybuteric acid. When these organisms then encounter aerobic conditions they will oxidize the stored organic polymers and other energy sources using electron acceptors (e.g. oxygen) from the aerobic environment and use the energy to form energy rich polyphosphate. The polyphosphate is stored so that the energy it contains may be used when anaerobic conditions recur, which allows the PAOs to displace other heterotrophic microorganisms that can not take advantage of the stored energy to thrive under anaerobic conditions. This relative energy advantage in the anaerobic environment leads to the dominance of PAOs over other phosphate uptake organisms which utilize oxygen as an electron acceptor. See Janssen, P. M. J., Biological Phosphorous Removal, Manual for design and operation, IWA Publishing (2002) at p. 17. When the PAOs use the energy stored in the polyphosphate in the anaerobic sub-zone, soluble phosphorous is released. When the PAOs return to the aerobic zone soluble phosphorous is absorbed and again converted to polyphosphate removing it from the aqueous phase and incorporating it as insoluble or particulate microbial biomass. If this biomass is then removed under aerobic conditions before the anaerobic environment is encountered, the phosphorous is removed from the system. Metcalf & Eddy, Wastewater Engineering—Treatment and Reuse, 4th Ed., Tchobanoglous, George et al., McGraw-Hill, Inc. (2003) at p. 623-627.
Recently, the Bio-P mechanism has been found to work if the aerobic process is replaced with an anoxic process containing nitrate and/or nitrite instead of molecular oxygen. Janssen, P. M. J., Biological Phosphorous Removal, Manual for design and operation, IWA Publishing (2002) at p. 16. However, the efficiency of the process using anoxic environment instead of aerobic environment is lower than that obtained when molecular oxygen in an aerobic environment is used. This occurs because it takes energy to extract oxygen from electron acceptors such as nitrate or nitrite and so the net production of usable energy from a substrate must be decreased by this amount (usually by about 40 percent when the electron acceptor is nitrate, see Janssen at pg. 20).
Despite this reduced efficiency, the addition of an anaerobic environment to a nitrate containing anoxic process, and the recycling of the anoxic liquid through the anaerobic environment, allows denitrifying PAOs to have a similar Bio-P selective advantage over normal, non-PAO denitrifiers. However, prior to the Applicants' discovery, this selective advantage was expected to disappear as the concentration of nitrate decreased to low levels because, compared to a normal non-PAO denitrifier, it would become more difficult for the PAO to acquire the additional electron acceptors it needs to generate the extra energy required to build and use the various PAO polymers. Thus, the concentration of nitrate or nitrite is rate limiting for PAO denitrifiers at significantly higher levels than it is for normal non PAO denitrifiers.
This rate limiting effect from concentrations of nitrate or nitrite is not a problem if other electron acceptors are available in sufficient quantities in the aerobic or anoxic environment. However, in environments with low electron acceptor concentrations, a cell would be less likely to get the additional ions it needs to grow and function compared to a normal denitrifier, and hence would not be competitive with such normal denitrifiers in that environment. The selective advantage which the anaerobic environment provided for PAO's would disappear. As the whole system approaches the conditions of an anaerobic environment (lower and lower concentrations of electron acceptors) the advantage of a separate anaerobic environment would be expected to disappear.
Despite the expectation that low concentrations of nitrate would make anoxic Bio-P ineffective, applicants have surprisingly found that if an anaerobic zone is added to or within the low oxygen organic waste biologically mediated conversion system described in U.S. Pat. No. 6,689,274 (Northrop et al.), and if the process liquid is recycled through the system, including the anaerobic zone, a significant transformation occurs whereby more soluble phosphorus is converted into particulate phosphorus. This transformation of soluble phosphorus into particulate form occurs even though the concentrations of molecular oxygen, nitrate, and nitrite are very low.
Applicants have therefore discovered an improved process for the biologically mediated conversion of organic waste and removal of nutrients from the waste. This process operates at low electron acceptor concentrations while maintaining high quantities of diverse populations of microorganisms in the process. The present invention addresses many of the problems associated with municipal, domestic, industrial, food industry, animal husbandry and other organic wastes, by providing an attractive and efficient means to resolve ecological problems associated with the treatment of organic wastes. More specifically, the present invention addresses the odor emission problem common to organic wastes as well as the problem associated with high nutrient effluent discharge concentrations through the efficient, substantially odorless, biologically mediated conversion of waste excrement materials or a vast array of other organic wastes into stable, economically and/or ecologically beneficial materials.
Thus, it is an object of the present invention to provide an improved process for the efficient, substantially odorless, biological treatment of organic waste.
It is another object of the present invention to provide an improved process for the efficient, substantially odorless, biological treatment of organic waste which converts a substantial portion of the soluble phosphorus into particulate form.
It is another object of the present invention to provide an improved process to create a biologically active, ecologically beneficial, substantially odorless humus material through the biologically mediated conversion of phosphorus containing organic waste, in which most of the phosphorus is captured in the humus material.
It is another object of the present invention to provide an improved process for the efficient, substantially odorless, biologically mediated transformation of organic wastes into suitable materials for recycling to the environment.
It is another object of the present invention to provide an improved process to create a biologically active, ecologically beneficial, substantially odorless humus material through the biologically mediated conversion of organic waste, particularly animal excrement.
It is a still further object of the present invention to provide a process to create a biologically active, and/or nutrient rich, organic soil.
It is a still further object of the present invention to provide a process to create a biologically active, and/or nutrient rich, feed material or supplement.
These and other objects will be apparent from the following description of the invention.